1. Field of the Invention
The present invention relates to an ink jetting device.
2. Description of Related Art
In recent years, non-impact type printing devices have superseded previously used impact type printing devices and have increasingly propagated in the market. Of these non-impact type printing devices, the ink jetting type printing device is more popular because it has the simplest printing principle and facilitates a color printing operation with high gradation. In this type of printing device, a drop-on-demand type printing device, in which only an ink droplet for printing is jetted, has rapidly increased in popularity in the market because of its high ink jetting efficiency and low running cost.
Examples of the drop-on-demand type printer include the Kyser type, as disclosed in Japanese Patent Publication No. 53-12138, and the thermal jet type, as disclosed in Japanese Patent Publication No. 61-59914. However, these types of printing devices have the following critical problems. With respect to the former, it is difficult to design the device with a compact size. With respect to the latter, ink is heated at a high temperature, thus requiring ink with a high heat-proof property.
To solve both of the above problems at the same time, a shear mode type, as disclosed in Japanese Laid-open Patent Publication No. 63-247051, is proposed as a new type of printing device.
FIGS. 3A and 3B show a shear mode type of ink jetting device. As shown in FIG. 3A, the shear mode type of ink jetting device 10 comprises a bottom wall 20, a ceiling wall 22, a rigid wall 26, an actuator wall 60 and an ink channel 24, which is surrounded so as to be sealed and defined by the above walls.
The actuator wall 60 is formed of piezoelectric ceramic material that is polarized in a Z-direction perpendicular to the ceiling wall 22 and the bottom wall 20, and it is firmly fixed to the bottom wall 20 and the ceiling wall 22. The wall surfaces 65 and 66 of the actuator wall 60 are provided with metal electrodes 68 and 69 at the lower side thereof and with metal electrodes 68' and 69' at the upper side thereof so as to be spaced from the metal electrodes 68 and 69. The metal electrodes 68, 68', 69 and 69' are electrically connected to a controller C.
As shown in FIG. 3B, when ink is jetted, the controller C controls the metal electrodes 68' and 69 to be grounded and applies a driving voltage V to the metal electrodes 68 and 69'. Through this operation, electric fields in opposite directions occur at the upper and lower portions of the actuator wall 60. Therefore, the upper and lower portions of the actuator wall 60 are displaced by thickness shear in such directions that the volume of the ink channel 24 is reduced. This deformation of the actuator wall 60 pressurizes the ink in the ink channel 24, so that an ink droplet is jetted from nozzles (not shown in this view) that intercommunicate with the ink channel 24.
In the ink jetting device described above, the metal electrodes 68' and 69 are grounded, and the metal electrodes 68 and 69' are supplied with the driving voltage. Thus, the metal electrodes 68, 68', 69 and 69' must be connected to the controller C. Accordingly, this ink jetting device has a disadvantage that a large number of connections between the controller C and the metal electrodes are required, and thus the manufacturing cost of the device is high.